Ruby is an elegant programming language that helps you write readable and reusable code.
SEO means Search Engine Optimization. It's an great leverage to make the difference.
Symfony is probably one of the most robust PHP frameworks with useful concepts and good practices
Varnish is an HTTP accelerator designed for content-heavy dynamic web sites as well as APIs
WebP is a relatively new format for images. Learn how to use it.
WordPress is, by far, the most popular content management system with a huge market.